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Oregon dam removal provides new information
SANDY, Ore. – The Marmot Dam on the Sandy River wasn't huge but it released major new information about river restoration when it was removed in October.
Before Portland General Electric breached the 50-foot dam it gave scientists a close look at a river digesting a vast amount of rocks, sand and gravel collected behind it over decades.
Some worried that the released sediment from behind the dam would suffocate salmon and block tributaries downstream. But the river has since digested the equivalent of about 150 Olympic-size swimming pools full of sediment.
"Never has this much sediment been released at once into such an active and hungry river," said Gordon Grant, a research hydrologist with the U.S. Forest Service's Pacific Northwest Research Station. He has studied the dam removal and given presentations on the results at conferences from Sacramento to Venice, Italy. He has been invited to talk in China.
"There's a global interest right now in river restoration," Grant said. "Marmot is certainly one of the best-documented and most spectacular examples of dam removal in the sense that the river was allowed to process the material itself."
The river has so far removed about half the material from behind the dam and is acting as a normal river should.
Some predicted the river would need two to five years to carry off half the sediment pile. It did it in months.
Federally protected coho salmon were swimming upriver to spawn the day after the dam crumbled.
The results may answer questions that have delayed removal of other dams.
But Grant cautioned against assuming removal of major dams on the Klamath River in southern Oregon and northern California would be as smooth. "That is a very different river system, he said.
The dam was built in 1913 to generate power but PGE decided in 1999 that updating it to help declining fish runs would cost more than its energy value.
A question was whether PGE should scoop out the sediment behind the dam or simply blow it up and let it go.
They blew it up.
Just in case, teams took wild fall chinook salmon from spawning areas to a hatchery, where the fry were raised to be released into the river to keep the stock going.
The dam never blocked salmon passage. A fish ladder allowed fish to get past the dam, and some fish advocates were disappointed to see the dam go because it kept hatchery-raised fish from mingling with wild salmon above the dam.
Biologists could sort the fish as they entered the fish ladder, allowing the wild fish upstream past the dam but keeping the hatchery fish out, making the upper reaches effectively a sanctuary for wild fish.
But Bill Bakke, executive director of the Native Fish Society, said the upside is that it 'lays more groundwork for a lot more dam removals, which have value for our rivers."
The Fish and Wildlife Department shifted its Sandy fish hatchery before the dam removal to raise fish stocks native to the Sandy, rather than the more generic hatchery fish.
Releasing native fish reduced the risk of diluting the genes of the wild fish population.
The removal allows faster, easier fish access to about 100 miles of river above the dam. The project also calls for removing a dam on the Little Sandy this summer, opening six miles of salmon stream that had been completely blocked.
Researchers have found that about 80 percent of the sediment that has washed downriver has spread out over the two miles below the dam, Grant said.
PGE is donating much of the land in the area to public use, and the U.S. Bureau of Land Management hopes to tie a trail network together along the river.
Information from: The Oregonian, http://www.oregonlive.com
Page Updated: Thursday May 07, 2009 09:14 AM Pacific
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